鄂尔多斯盆地长7段致密砂岩储层特征及成因机理

Characteristics and formation mechanism of Chang 7 tight sandstone reservoir in Ordos basin

为了精确表征长7段致密砂岩储层特征及研究致密储层成因,在盆地尺度范围内,综合利用常规镜下薄片观察、高压压汞实验、XRD分析手段,并结合高精度TRA物性实验,精确表征了长7段致密砂岩储层的岩石学特征及储集性能,在此基础上分析了致密储层成因,认为致密储层成因主要有机械压实及压溶作用、各种类型的胶结作用、交代作用、沉积微相的控制作用以及填隙物的影响.研究结果表明:长7段致密砂岩储层以岩屑长石砂岩和长石岩屑砂岩为主;石英含量较高,质量分数平均值为40.4%,具有较强的可压裂性,有利于后期的压裂开采;填隙物中水云母的含量较高,质量分数平均值为10.4%,导致长7段物性变差;孔隙类型以长石溶孔为主,占总孔隙的60%,排驱压力高,中值压力平均为7.72 MPa;喉道细小,孔喉结构复杂,物性较差,孔隙度均值为8.55%,渗透率均值为0.21mD.

Based on the conventional thin section observation, high pressure mercury experiment, XRD and high-precision TRA experiment, the petrological characteristics and reservoir property of Chang 7 tight sandstone reservoir were precisely characterized on a basin scale. The formation mechanism of tight sandstone reservoirs were then analyzed on this basis, and factors including mechanical compaction, pressure solution, cementation, metasomatism, the control of sedimentary micro-facies and interstitial material were found to play a role in the formation process. The results show that consisted mainly by arkose and lithic arkose sandstone, Chang 7 tight sandstone reservoir is prone to be fractured and favorable for later recovery due to high content of quartz, whose average value is 40.4% ; the physical property is poor due to the high hydromica content, whose average value is 10.4% ; the main pore type is feldspar dissolution, which accounts for 60% ; the displacement pressure is high and the median pressure average value is 7.72 MPa; the pore throat is small in size and complex in structure; the average porosity is 8.55% and the average permeability is 0.21 mD.